1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor substrate having a silicon film on a transparent insulator substrate.
2. Description of the Related Art
As a semiconductor substrate that enables high performances of a semiconductor device, an SOI (Silicon On Insulator) substrate is attracting attention (see, e.g., Japanese Patent No. 3048201 or A. J. Auberton-Herve et al., “SMART CUT TECHNOLOGY: INDUSTRIAL STATUS of SOI WAFER PRODUCTION and NEW MATERIAL DEVELOPMENTS” (Electrochemical Society Proceedings Volume 99-3 (1999) p. 93-106).). That is because adopting an SOI structure to bury an oxide film below a single-crystal silicon thin film enables reducing a parasitic capacitance, improving an operating speed, and suppressing a power consumption.
When the SOI substrate is utilized as an optical device, a support substrate that is bonded to a silicon substrate must be a transparent insulator substrate, and from the viewpoint of a cost reduction, a borosilicate glass substrate or a crystallized glass substrate is also examined besides a quartz substrate or a sapphire substrate as such a substrate.
However, since each of these transparent insulator substrate has a thermal expansion coefficient greatly different from that of a silicon crystal, there occurs a problem that a bonded substrate or an SOI substrate is broken or cracked when a manufacturing process of the SOI substrate includes a high-temperature process. Therefore, a reduction in temperature in the entire manufacturing process of the SOI substrate is demanded, and a reduction in temperature must be achieved in a process of forming a gate oxide film after forming an SOI film on a transparent insulator substrate in particular.
In recent years, as a low-temperature oxidation technology that can substitute for thermal oxidation requiring a high temperature, an oxidation method using highly-concentrated ozone (Akira Kurokawa et al., “Interface Structure of Ultrathin SiO2 Film Formed by Highly-concentrated Ozone” (Bulletin of the Electrotechnical Laboratory, Vol. 63, No. 12, p. 501-507, (2000)).) or an oxidation method using a microwave-excited plasma (Tadahiro Ohmi et al., “Low-temperature Formation of Silicon Oxide Films using Microwave-excited Kr/02 Plasma”, “OYO BUTURI” (Vol. 69, No. 10, p. 1200-1204, (2000)).) is also proposed, but these techniques require a special oxidation system different from that in a conventional apparatus.